Citric Acid → 4-Bromo-2-(trifluoromethyl)benzenethiol

Participants

Reaction Conditions

Reaction Steps

4-Bromo-2-trifluoromethyl-benzenesulfonyl chloride (375 g, 1.16 mol) was dissolved in toluene (1.5 L) and a solution of triphenylphosphine (994 g, 3.79 mol) in toluene (1.5 L) was added at 5-10° C. within 45 min. The yellow suspension was stirred at 0-5° C. for min, then water (360 mL) was added at 5-12° C. (strongly exothermic) and the resulting colorless suspension was stirred for 20 min at room temperature. After filtration, the precipitate was washed with toluene (1 L). The combined organics were extracted with a potassium hydroxide solution (1M in water, 2.8 L). During extraction, 3 layers were formed. The upper layer was discarded, the other two were washed with toluene (1 L). The aqueous phase was acidified to pH 3-4 by addition of citric acid (280 g, 1.46 mol). After addition of n-heptane (1 L), the precipitate was filtered off and washed with n-heptane (500 mL). The layers of the combined filtrate were separated and the aqueous phase was extracted with n-heptane (1.5 L). The combined organic extracts were dried over sodium sulfate. Silica gel (250 g) was then added, the slurry was stirred for 10 min at room temperature, filtered and the filtered silica gel washed with n-heptane (1 L). The combined filtrate was concentrated and dried in vacuo at 45° C. to afford 291.2 g (98%) of the title compound as a colorless liquid that was used without further purification in the next step. MS (EI): m/z=256.9, 254.9 [M+H]+. 1H NMR (CDCl3, 400 MHz): δ 3.76 (q, J=2.8 Hz, 1H), 7.26 (d, J=8.3 Hz, 1H), 7.48 (dd, J=2.0 Hz, 8.5 Hz, 1H), 7.75 (d, J=1.9 Hz, 1H).

Provenance & Evidence